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Sky watch: String of planets dots the sky at dusk

A beautiful string of planetary pearls shines at dusk the week of July 4 through July 10 and the week after that, and stargazers with clear skies will be able to see five planets - and the moon - all at one time.

Head outdoors just after sunset and, if you've got a clear sky and an open view low toward the west-northwest, you should see the planet Mercury. This elusive rocky world is seldom easy to spot, so we should take advantage of its location. You might find that binoculars will help you find it.

Above Mercury is the brilliant white planet Venus. This world shines so brightly because it's shrouded in highly reflective clouds.

Above and to the left of Venus, we find the Red Planet, Mars. You may remember in January when Mars was relatively close to Earth and appeared much brighter in our sky; now it's significantly farther away and appears rather faint - especially when located in the same celestial neighborhood as Venus.

The final pearl in the planetary chain is Saturn, the Ringed Planet, now located not that far above and to the left of Mars. Saturn lies more than 900 million miles from us, but appears brighter than Mars because its ring and large cloudy surface reflect so much sunlight back to our eyes.

Over the next week or so, pay close attention to the relative positions of these four worlds. Each day at dusk, Mercury will appear slightly higher above the horizon; and Venus, Mars and Saturn will seem to close in more on one another. On July 12, look for the thin crescent moon just below and to the left of Mercury. The following day, a slightly thicker crescent will lie between it and Venus, and on July 14, it will appear to make a stunning sight just below Venus.

Notice how all these worlds seem to form an arc across the sky. There's nothing odd about that. It's called the "ecliptic," and it's formed by the projection of the Earth's orbit (around the sun) onto the sky. And since most solar system bodies orbit the sun in roughly the same geometric plane - they came from the same spinning disk of material, after all - they always appear to lie on or near the ecliptic.

So where's the fifth planet we can see at dusk, you ask? Think about it!

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